Good Telephoto lens for Rebel XSI

I'm new to the forums here and am just starting getting into the DSLR world. I've had point and shoot in the past and currently have a Kodak P712. I am now going to get the Canon Rebel XSI and just want to know what a good telephoto lens would be to go with this. Right now my Kodak has a "10X" zoom (36mm-432mm equivalent) and I would like a telephoto lens that could have that same "zoom power." I've read a lot of posts and just cannot find one that has the same situation I am in so I was wondering if any of you could help me out. I was considering the Canon EF 70-300mm f/4-5.6 IS lens but I'm just wondering if this would be more of a lens than I need. I do want the image stabilization in the lens and, like I said, a zoom comparable to the current Kodak I have. Thank you very much for any help or suggestions you can offer.

Firstly, you need to consider what is more important to you...a large range of zoom, the long end of the zoom or image quality. And what is your budget?

For the most part, the greater the zoom range (10x, 12x etc) the more compromises had to be made in it's design...which ends up giving you lower image quality. Most of us who use SLR cameras consider a bigger zoom range to be a bad thing...which is the opposite of people thing with their smaller digital cameras. Of course, with an SLR type camera, you can switch the lens and use something more appropriate to what you are shooting...with a small 'digi-cam' you can't switch the lens.

In the lowest price range, we have the 70-300mm range of lenses. Canon makes a cheap version, as does Tamron & Sigma. They are alright but not great. The do well in great light but really struggle in mid to low light. The Canon 70-300mm IS, is a step up. Not only does it have IS but I've heard that it's optically better than it's cheaper cousins. I forget the price, but I remember it being expensive.

There are 4 Canon lenses that are 70-200mm. Less zoom range but much, much better quality. The price ranges quite a bit as well, for these 4 lenses.

If you want a convenient lens, with a wide zoom range, you will be sacrificing some quality...but I'd still think that it would be a good step up from your Kodak digi-cam. Some examples would be the 18-200mm or the 28-300mm.

I tell you what, I'm absolutely thrilled with my EF 70-200mm f/2.8L. The thing has sick resolution and clarity. I'm more impressed with it than I am my 24-70mm f/2.8L in terms of contrast, clarity and general optical performance.

Until you really know what you want ...The Canon EF 70-300 f/4 -5.6 IS USM is a great first lens. I have lenses that out perform it in my kit now yet I hesitate to sell this one off. It's two shortcomings are #1 it is a little slow in Max Aperture being f/4 at 70 and f/5.6 at 300 and #2 it's AF is slowere than its Ring type USM cousins.

optically it's not to shabby and very close to being an L class lens. I think this lens is often overlooked by those seeking an 300 mm lens that is affordable at less than 600 USD.

Here's a description of it and some details.

The Canon EF 70-300mm f/4-5.6 USM IS is a brand new lens replacing the old EF 75-300mm f/4-5.6 USM IS which was the first Canon IS lens to hit the market back in 1995. On APS-C DSLRs such as the EOS 350D/Digital RebelXT (used for testing) the field of view is equivalent to 112-480mm. It's a full frame lens so it is compatible to all EOS cameras out there.
The lens has been improved in a number of ways. The most significant change is a redesign of the optical construction which now features a UD element - something that we usually only see in Canon L grade lenses.
The AF speed has been significantly improved to a very decent level without being as fast as ring-type USM lenses. Thanks to a micro-USM drive the noise level is very low. The lens does not feature FTM (full-time manual focusing in AF mode) though. Due to the rather slow max. aperture the EOS 350D had sometimes a hard time to find a really accurate focus at 300mm - this is not specific to this lens though.
One key selling factor for this lens is naturally the Image Stabilizer (IS). Camera motion is detected by 2 gyro sensors which measure the angle and speed of the shake. This information is used to shift a lens group off the optical axis (basically a forced decentering) to counteract this motion. The result is a significant improvement of handholdibility under extreme conditions. Canon improved the efficiency of the mechanism to an equivalent of 3 f-stops (up from 2 f-stops).
The IS now offers 2 different modes (instead of just one):